Packetized data communication is now being used in a wide variety of applications, which includes such diverse elements as data communication, control information, and digitized/packetized voice. As a result, conflicting demands are being placed on packet switches in order to handle such diverse traffic. An example of such diverse packet streams is shown in the context of FIG. 1, wherein a code division multiple access (CDMA) cellular communication system is illustrated in block diagram. A CDMA system transmits/receives data at the relatively slow rate of approximately 8 Kbps over a spread spectrum signal between a mobile unit and a cell site. A transceiver at the cell site sends/receives the spread spectrum signal and translates the content of the signal into packets. A speech processor then translates the packets into a digital 64 Kbps pulse code modulated (PCM) stream, as used in standard digital switching.
FIG. 1 illustrates such a system in the context of U.S. Pat. Nos. 5,363,309, and 5,438,565, which are both owned by the assignee of the current application, and are incorporated herein by reference. In this illustration, there is a central office switch 1, which is connected to a public switched telephone network (PSTN) 3, a telephone 4, and a plurality of CDMA cell sites 5-11. CDMA cell sites 5-11 send and receive spread spectrum signals and translate the signals to/from the packetized stream. CDMA cell sites 5-11 are connected to switch 1 via a plurality of trunks 13-19, connected to an equal number of digital facility interfaces (DFI) 21-27 at switch module (SM) 33 of switch 1. DFI's 21-27 provide termination of the digital trunks to and from cell sites 5-11, as is known in the art, and, therefore, will not be discussed further. Executive call processor (ECP) network 29 connects to switch 1 in cell sites 5-11 for exchange of control data via DFI 30, as is known in the art, and described in The Bell System Technical Journal, vol. 58, number 1, January, 1979.
Switch 1 is illustratively a distributed control, ISDN electronic telephone system, such as the system disclosed in U.S. Pat. No. 4,592,048, Beckner, et al., which issued May 27, 1986. Alternatively, switch 1 may be a distributed control digital switch such as a 5ESS.RTM. switch manufactured by AT&T Corp. and described in The AT&T Technical Journal, vol. 64, number 6, July/August, 1985, pages 1303-1564. The architecture of switch 1 includes communication module 31 as a hub, with switch module 33, other switching modules (not shown for clarity), and administration module 35 emanating therefrom. Switch module 33 terminates analog and/or digital subscriber lines through line units, such as line unit 37, and analog or digital trunks through trunk units, such as trunk unit 39. Line unit 37 provides communication with telephone 4 via line 41. Trunk unit 39 provides communication with public switched telephone network (PSTN) 3 via trunks 43. Administration module 35 provides coordination of the functional components of switch 1 and human/machine interface.
Switch module 33 includes a switch module processor (SMP) 44, a timeslot interchange unit (TSIU) 45 and packet switch unit 47. SMP 44 provides control and coordination of the various components of switch module 33. TSI unit 45 provides interchange of 64 Kpbs PCM or 64 Kbps clear channel among the units in switch module 33. Switch module 33 may also contain other units, but, for purposes of clarity, these other units are not shown.
Packet switch unit (PSU) 47 includes packet interface 48, packet handlers 49-55, and speech processors 57 and 59, which are all connected to packet bus 61. There may be other units performing similar (or even dissimilar) functions connected to packet bus 61, but these are not shown for clarity. Packet interface 48 communicates with SMP 44 to provide configuration and control information to the other components in PSU 47. Packet handlers 49-55 perform a frame relay function; that is, they receive packets from cell sites 5-11 and a delivery address from executive control processor (ECP) 29, and relay the packets onto a packet bus 61. Speech processors 57 and 59 "listen" to packets on packet bus 61 (by reading address headers), determine which packets are for themselves, buffer them, and translate these packets into switchable 64 Kbps PCM. In the reverse direction, speech processors 57 and 59 receive 64 Kbps PCM uncoded speech, translate it into CDMA packets, add a two-part address, and send the packets out on bus 61.
According to this system, a mobile telephone in car 54 initiates a CDMA call in cell 5, which call is then set up over radio channels between mobile 54 and cell site 5. A speech processor 57 at switch 1, in this example, is assigned to the call and its address is given to cell site 5. As signals arrive at cell site 5, they are packetized. Packets are multiplexed into packet pipes, which are themselves multiplexed and then sent over trunk facility 13. DFI 21 receives the multiplexed trunk facility 13, then demultiplexes the packet pipes and sends the packet pipes to packet handler 55 on a path through TSIU 45 that is semi-permanently set up ("nailed up") between DFI 21 and packet handler 55. As packets arrive through TSIU 45 to packet handler 55, packets are demultiplexed from the packet pipes and placed on packet bus 61. Packets are then received by speech processor 57. Speech processor 57 accepts all packets for itself and performs a conversion to 64 Kbps PCM. Speech processor 57 is connected through TSIU 45 to line unit 37, to telephone 4 (alternatively through trunk unit 39 to PSTN 3).
In this system, packet handler 55 receives a CDMA packet stream from TSIU 45. From cell site 5, such packet stream is "polled," in that packet handler 55 periodically checks to determine if there are any CDMA packets to process from cell site 5. Additionally, packet handler 55 also has packets delivered to it from packet bus 61. Packets arriving from packet bus 61 cause an interrupt to be generated. Further, as will be discussed below, communication between packet handler 55 and packet interface 48 is an interrupt-driven packet stream. Thus, both interrupt-driven packet streams are serviced by packet handler 55 before the CDMA packet stream, which causes the CDMA packet stream to become overloaded by delaying the CDMA packet stream to an unacceptable degree. CDMA packets are very time sensitive, because they contain digitized voice samples. If many of these digitized voice samples are lost or delayed, the voice call looses quality and may ultimately be torn down because of timeouts, etc. Therefore, it is critical that the voice packets be handled in a timely manner. However, given the nature of interrupts, packets that work on an interrupt basis may cause the polled CDMA packets to be delayed.
Therefore, a problem in the art is that interrupt-driven packets may cause unacceptable delays in processing polled packets.